Electrical testing system



Nov. 28, 19-39. F F; BLQU T 2,181,560

ELECTRICAL TESTING SYSTEM Filed July 1, 1937 NEGATIVE RES/STANCEINVENTOR F E. BLOUNT 'Arro NE) Patented Nov. 28, 1939 .PATENT OFFICE2,181,560 7 ELECTRICAL TESTING SYSTEM Frank EsBlount cedar Grove, N. 1.,assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y.,a corporation of New York Application July 1, weas l-m1 No. 151,406

19 Claims. (curs-175.2)

This invention relates to testing devicesv and particularly to means fortesting the continuity of electrical connections.

It is'the object of the invention to provide a 1 5 reliable arrangementfor testing the continuity of an electrical connection, the closedcircuit impedance of which maybe non-linear in character. v

Thisjinvention is a ,circuittesting .device .com-

' prising a source .of .alternating .current, atest .relay and agas-filled tube,.the control element of the tube being so connected tothe circuit path under test .thatthe test relay is operated only if thecircuit pathis continuous.

A featureof the invention is acircuit. testing :device comprisinga.source of alternating current, a test relay and a gas-filled tube, thecontrolelement of the tubebeing so connected to the circuit path'under'test that the testgrelay is operated only if the circuit path iscontinuous, and moreover vwithout operatively afiecting any electricalapparatusincluded-in the circuit.

Another-feature of 'the invention is "a'circuit testing devicecomprising a source of alternating current, a test relay and 1a'gas-filledtube for testing the continuity of a connection, the closedcircuit impedance'of which is non-linear "in character, the controlelement-ofthe tube-being so connected to the' circuit path= under'testthat the test relay is operated onlywhen'the path is continuous.

A further feature of the invention is'a circuit testing'devicecomprising a source of alternating current, a test relay andagas-filledtube for testing the continuity ofa circuit path which includes acircuit element ofieringa hightimpedance to impressed differencesinpotentialbelow a critical value and a very much reduced impedance toimpressed differences in potential equalto or greater than thiscritical'value.

A clear and complete understanding of the invention will be facilitatedbythe consideration of testing devices arranged in accordance with theinvention, four such arrangements being shown schematically in thedrawing which forms a part of this specification. The'invention is notlimited in its application to the specific arrangefilled tube l3. -relayI0 is energized by the current in the anode- "L, andin the markeratesting device comprising a test relay and a gas-filled tube.

,Fig. 1 also shows the ringer and ringing con- ,densernormallybridgedacross the conductors of, a line ,servingasinglesubscriber; and 5 .Figs..5, 6 and 7 show alternative arrangements.ofringing-apparatus normally bridged across the .conductors. atthestations of a multi-party line.

,The subscribersstation connected to line L is 0 represented in Fig. 1.by the ringer and ringing 1 condenser which are. normally Lbridgedacross a line which serves a singlev subscriber, the other stationapparatus being omitted. The selector switches IS and FS may be of,anyknown type ar- .rangedjfor vmarker control. Reference may be 15 hadtothe patents of W. W. Carpenter, No. 2,093,117 dated September 14, 1937and No. 2,089,921- dated August 10, 1937 for a complete description ofan automatic telephone system comprising. marker controlled switches forestablishing connections with called lines. The

marker is represented by the broken line enclo- ,throughswitches IS andv FYS to the line L is tested by connecting the testing apparatus to theconductors of switch IS.

" Upon v:vconnection of the testing apparatus .shown in Fig. 1 throughconductors II and I2 to the conductors of switch vIS, and assuming the.connection through switches IS and FS and .over line L to thesubscribers station to be continuous there is a circuit from ground,through conductor ll, upper contacts of switches IS and FS, .over lineL, through the ringing condenser l8 and ringer I!) at the subscrib- 40ers station, lower contacts of switches FS and IS, conductor l2, upperwinding of transformer l6, and through condenser M to ground. The lowerwinding of transformer 16 is connected to a source of alternatingcurrent l5 to produce a current in the above traced test circuit. Thiscurrent is not strong enough tooperate the ringer but the resulting dropin potential across condenser M is'sufiicient to cause breakdown betweenthe control electrodes and ionization of the gas inthe three-elementcold cathode gas- 1 Upon ionization of tube l3, test cathode circuit;-and'the operation of relay [0 closes a circuit which frees the markerfor use "'55 on other connections. The resistor ll limits the currentover the line after breakdown of the tube. If, however, the connectionto and through line L is not continuous, the impedance of the testcircuit is very much higher, its value being dependent upon the capacitybetween the conductors up to the open point and the capacity of each ofthese conductors to ground; and the current in the test circuit producesa drop in potential across condenser l4 which is insufiicient to causebreakdown between the control electrodes of tube [3. does not operate,the switches IS and F8 are released and the marker operates further toes tablish a connection with the called line L through another one ofthe available switch paths. The transformer ratio and size of condenserM are such as to cause operation of the .tube and test relay when aconnection and line of maximum closed circuit impedance is being testedand prevent operation of the tube and relay when the open circuitimpedance is a minimum.

If the line being tested is a party line, the signaling bridge at eachsubscriber's station may consist of the ringing condenser and a relay,each relay being efiective when operated to connect an associated ringerto the one or the other of the line conductors. When testing such aline, these relays do not respond to the test current and the testproceeds as above described- If the line being tested is a party line,the signaling bridge at each station may comprise a gas-filled tube orother circuit element having a non-linear impedance characteristic. Thesignaling bridge shown in Fig. 5 comprises a three-element cold cathodegas-filled tube 58 which breaks down upon closure of the test circuitover conductors H and I2 of the marker in Fig. 1; and the current in thetest circuit charges condenser M to cause breakdown of tube l3 andoperation of test relay II]; but this current is insuflicient to operatethe ringer 59. The signaling bridge shown in Fig. 6 is similar to thatof Fig. 5 except that it is reversed with respect to the conductors ofthe line L. The signaling bridge shown. in Fig. 7 comprises a boronelement 11 in serieswith a condenser 18 and a relay 19 which relay whenoperated connects a ringer to the one or the other of the conductors ofthe line. When the test circuit is closed over conductors H and I2 ofthe marker in Fig. 1, the impedance of the boron element 11 is reducedsufficiently to cause operation of the tube l3 and relay l0 withoutpermitting operation of the relay [9. v

The testingapparatus shown in the marker of Fig. 2 comprises a testrelay 2!], a three-element hot cathode gas-filled tube 23, a condenser24, resistors 25, 26 and 21 and a source of alternating current 28. Tube23 is normally biased by a battery 29 connected between the cathode andgrid to prevent the operation of relay 2!]. The condenser 24 andresistors 25 and 26 form an impedance network connected in series withthe source 28 and. the circuit path under test, the junction pointbetween resistors 25 and 26 being connected to the grid of tube 23. Ifthe connection to the called line is continuous, part of the drop inpotential across condenser 24 (that is, the drop in potential throughresistor 25) is impressed on the grid and overcomes the negative bias toinitiate current between the anode and cathode and thereby cause theoperation of test relay 2!]. The condenser 24 is of such a capacity andthe resistors 25, 2B and 21 of such Since in this case relay IOresistances that relay 2!] is not operated when the minimum open-circuitimpedance is encountered but is operated when the maximum closed-circuitimpedance is encountered. This testing apparatus will operatesatisfactorily when testing any of the line conditions represented inFigs. 1, 5, 6 or 7, the ringer or ringing relay at each station beingnon-responsive to the test current.

The testing apparatus shown in the marker of Fig. 3 comprises a testrelay an, a three-element cold cathode gas-filled tube 33, a condenser34, resistors 35 and 36, a source of alternating current 3! and anauxiliary relay 38. Relay 38 is operated in a circuit, not shown, priorto the closure of the testing circuit and is held operated under controlof test relay 30. Upon connection of the source 31, condenser 34 andresistor 35 in series to the conductors of a switch IS, the drop inpotential through condenser 34 is suificient if the connection to thecalled line iscontinuous to cause breakdown between the controlelectrodes of tube 33; and the resulting ionization of the gas initiatescurrent between the anode and cathode to operate relay 3!]. Theoperation of relay 30 causes the release of relay 38, allowing themarker to be disconnected. The resistor 35 and condenser 34'are of sucha character as to prevent operation of relay 30 when the minimumopen-circuit impedance is encountered and to cause operation of relay3!! when the maximum closed-circuit impedance is encountered. Theresistor 35 limits the current over the line after breakdown of thetube. This testing apparatus will operate satisfactorily when testingany of the line conditions represented in Figs. 1, 5, 6 or 7, the ringeror ringing relay at each station being non-responsive to the testcurrent.

The testing apparatus shown in the marker of Fig. 4 comprises a testrelay 40, three-element hot cathode gas-filled tube 43, a transformer44,

condenser 45, source of alternating current 46 and resistor 41. Tube 43is normally biased by a battery 49 and potentiometer 48 to prevent op.eration of relay 4 Upon connection of source 46, resistor 41, andcondenser 45 in parallel with the upper winding of transformer 44, inseries to the conductors of a switch IS, the dropin potential acrosscondenser 45 is impressed across the upper winding of transformer 44 andinduces a difference in potential across the lower winding of thistransformer. If the connection to the called line is continuous, thedifference in potential across condenser 45 is sufficient to overcomethe normal bias of tube 43 and initiate current between the anode andcathode to operate test relay 40. A 60 cycle alternating current sourceis shown in the anode-cathode circuit but a direct current source may beused. If the connection is open at any point, relay 40 is not operated.The resistor 41, condenser 45, and transformer .44 are of such acharacter as to prevent operation of relay 4!) when the minimumopen-circuit impedance is encountered and to cause operation of relay 40when the maximum closed-circuit impedance is encountered. This testingapparatus is adapted to test any of the line conditions represented inFigs. 1, 5, 6 or '7, the ringer or ringing relay at each station beingnon-responsive to the test current.

What is claimed is:

l. A testing device for testing a circuit path, said device comprising asource of alternating current, a condenser connected in series with saidsource and the circuit path under test, a

three-element gas-filled tube of the cold 'electrode type, the controlelementsofsaidtube'being connected to opposite terminals of said con-;denser, and a test-relay,-said relay being connected in series with theanode and one'of the control elements of said tube.

2. A testing apparatus 'for testing the impedance of a circuit path,said apparatuscomp-rising a source of alternatingcurrent,.'-a:condenser, a three-element gas-filled tube'iand atestrelay, said relay being connected inseries withrthe anode and cathode ofsaidtube,tand*saidcondenser being connected in series with said sourceand the circuit path which is beingttested; the

grid and cathode of said tube being connected to opposite electrodes ofsaid condenser so that the potential' of the grid with respect .to thecathode depends upon the difierence in potential between saidelectrodes.

3. A testing apparatus for testing the continuity of a circuit path,said apparatus comprising a source of alternating current and acondenser connected in series' with the path undergoing series with saidsource and the circuit path under test, a three-element hot cathodegas-filled tube, the grid and cathode of saidtube being connected toopposite terminals of said condenser as to be electrically affected bythe drop in potential through said condenser, and a test relayconnectedinseries withthe anode and cathode of said tube.

5. Apparatus for testing a circuit path, comprising a transformer, asource of alternating current connected to the primary winding of saidtransformer, a condenser connected in series with the secondarywindingof said transformer and the circuit path which is being tested, athreeelement gas-filled tube of. the cold electrode type,

the control elements of said tube being connected to opposite terminalsof said condenser, and a test relay connected in series with the anodeand one of the control elements of said tube.

6. Apparatus for testing a circuit path, comprising a source ofalternating current, a condenser connected in serieswith said source andthe circuit path under test, a three-element'hot cathode gas-filledtube, the cathode and grid elements of said tube being connected toopposite terminals of said condenser, and a test relay connected inseries with the anode and cathode of said tube.

'1. In a combination according to claim 6,

7 means for biasing the grid of said tube with "denser-and zanotherwinding connected between the grid and cathode .of said tube, and a testrelay connectedin the anode-cathode circuit of said tube.

.10.'I.na switching system, means for testing the .circuitpathestablished through a train of I. switches, said circuit path includingseries capacitance, said testing means comprising a source ofalternating current and a condenser connected in .series with thecircuit path undergoing test, a

three-element gas-filled tube, a test relay con- :nected in series withthe anode and one of the controlelementsof said tube, and means conmentsof said tube so that the drop in potential acrosssaid condenser isimpressed on said con- .trol elements.

111. In combination a circuit path which is .:heing tested, electricalapparatus included in said circuit path, and testing means comprising asource of alternating current, a condenser con- .nected in series withsaid source and circuit path,

a three-element gas-filled tube, the grid and necting said condenseracross the control eleconnected in series with the anode and cathode'Of:.S3/id tube; said condenser being effective to prevent the operationof said electrical apparatus during the test, and the drop in potentialacross said condenser being effective if said circuit path is continuousto initiate current in the anodecathode circuit to operate said testrelay.

12. In combination, a circuit path which is being tested, a circuitelement in said circuit path, the impedance of said element beingnon-linear in character, and testing means adapted to test thecontinuity of said circuit path, said testing means comprising a sourceof alternating current, a condenser connected in series with said sourceand said circuit path, athree-element gas-filled tube, thegrid andcathode of said tube being connected to opposite terminals of saidcondenser so I that the drop in potential. across said element iseffective if said circuit path is continuous to initiate current betweenthe anode and cathode, and a test relay in series with the anode andcathode.

13. In combination, a circuit path which is being tested, circuitelements including a gasfilledtube connected in series in said circuitpath,

and testing means for testing said circuit path, said testing meanscomprising a source of alter nating current, a condenser connected inseries with said source and said circuit path, a threeelement gas-filledtube, means connecting said condenser across the control elements ofsaid three-element tube, said first-mentioned gasfilled tube becoming aconductor upon connection of said source to said circuit path if saidcircuit path is continuous, the drop in potential across said condenserbeing thereupon increased sufficiently to cause the energization of saidthreeelement gas-filled tube, and a test relay connected in series withthe anode and one of the control elements of said three-element tube.

14. In a testing device according to claim 1, an impedance elementconnected in series with said control elements and said circuit path forlimiting the current in said circuit path upon ionization of the gas insaid tube.

a resistor connected in series with said circuit path and the controlelements of the three-element tube for limiting the current in saidcircuit path upon said tube becoming a conductor.

17. A device for testing the continuity of a circuit path, said pathincluding a non-linear impedance, said device comprising a three-elementgas-filled tube, a source of testing potential, a capacitor, a resistor,said source and capacitor being connected in series with said circuitpath, said capacitor and resistor in series being bridged across thecathode and control elements of said tube, and a relay and a source ofpotential connected in series with the anode and cathode elements ofsaid tube,

18. A testing apparatus for testing the continuity of a circuit pathincluding series capacitance, said apparatus comprising a source ofalternating current and a condenser connected in series with the pathundergoing test, a three-element gasfilled tube of the cold electrodetype, the control elements of said tube being connected to the opposingelectrodes of said condenser, a source of current, and a relay connectedin series with the anode, said source and one of said controlelectrodes.

19. In a telephone system, subscribers stations and lines,switchescomprising movable contacts, means comprising a marker for controllingthe operation of one or more of said switches to establish a connectionwith a desired one of said subscribers lines, and means for testing thecontinuity of the connection through said switches, said testing meanscomprising a three-element gas-filled tube of the cold electrode type, asource of alternating current, a condenser, a test relay, meansconnecting said condenser and source of alternating current in serieswith the conductors of the switches included in said connection, thecalled line and subscribers station equipment also being connected inseries with said source and condenser if the connection through saidswitches is properly closed, means connecting said condenser across thecontrol elements of said tube so as to impress the drop in potentialthrough said condenser on said control elements, and a source of currentconnected in series with said relay and the anode of said tube and oneof the "control elements, the drop in potential throughsaid condenserbeing large enough to cause breakdown of the tube and operation of saidrelay only if there is a closed circuit through said switches andthecalled line. l

FRANK E. BLOUNT.

